The present invention relates to a color image forming apparatus, and more particularly to an image processing apparatus for performing suitable color reproduction in a digital color copying machine, a printer, etc.
In a conventional digital color copying machine, the reflectance of a color image on an original is read by color-separating pixels into R (red), G (green) and B (blue) and is converted to digital image data of three colors, R, G and B. The three-color digital image data is subjected to color correction processes such as a density conversion process, a background color elimination process, a black addition process, and a masking process, and thus digital image density data of four colors, C (cyan), M (magenta), Y (yellow) and K (black), is obtained.
Based on the four-color digital image density data, a dot image that is a digital image is recorded on copying paper.
With the development of device-independent color reproduction technology, various color gamut compression methods have been proposed. In particular, in recent years, with the prevalence of digital cameras, household scanners and printers, not only office users but also personal users have more opportunities to treat color image data between devices with different expressible color regions.
There is a strong demand for image data processing which can be performed by a preferable color gamut compression method without adjustment by non-skilled users.
Jpn. Pat. Appln. KOKAI Publication No. 7-298073, for instance, proposes a method wherein a user designates the limitations to the hue and chroma in the clipping of a color gamut. However, general users do not have a definite criterion, for example, on the concept “color is dense”, as to whether this means that the chroma is high or the brightness is low. It is very difficult to demand that the users perform the adjustment of this publication.
The article titled “Adaptive color gamut mapping method based on image dependency” appearing in the “The Journal of The Institute of Image Electronics Engineers of Japan”, Vol. 29, No. 5 (2000), shows a method of automatically adjusting the weight of chroma and brightness in accordance with image modes. However, it is most desirable to perform color gamut compression suitable to an original in a default mode (generally a character/print photo mode).
As has been described above, according to conventional color gamut compression methods, it is difficult for general non-skilled users to achieve desired color reproduction with respect to an original which is an object of printing-out, and the users have to perform time-consuming procedures.